EP3026071A1 - Stabilised polyurethane dispersions - Google Patents

Abstract

The present invention relates to aqueous polyurethane dispersions preparable by a process comprising: (i) preparing a PU prepolymer from a polyol blend and at least one organic polyisocyanate, wherein the polyol blend (a) comprises at least 40-95 weight percent a polyester polyol having a melting point T m of greater than 0 ° C; (b) 0.1-5% by weight of at least one polyol having at least one ionic or potentially ionic hydrophilic group; and (c) 0.5-10 wt% of at least one nonionic polyether polyol, wherein the polyether polyol is a polyalkylene glycol homo- or copolymer having a content of ethylene oxide units of less than 50 mol%; wherein the polyurethane prepolymer contains less than 5 weight percent ethylene oxide units; and (ii) dispersing the polyurethane prepolymer into a continuous aqueous phase such that a stable emulsion of the polyurethane prepolymer is formed, and (iii) chain extension of the prepolymer by means of a chain extender. The polyurethane dispersions obtainable in this way have a wide range of uses, such as, for example, adhesives, sealants and coating compositions, but also detergents and cosmetics.

Description

The present invention relates to water-based polyurethane dispersions in which the polyurethane is stabilized by a combination of ionic and non-ionic groups which are incorporated directly into the polyurethane during the polymerization. The dispersions are prepared by homogenizing the corresponding polyurethane prepolymer by a high shear process in water to produce an emulsion, followed by chain extension of the prepolymer. The polyurethane dispersions obtainable in this way have a wide range of uses, such as, for example, adhesives and coating compositions, but also detergents and cosmetics.

Polyurethane dispersions are used on a large scale for industrial adhesives and used for example in the footwear and furniture industry. The most important process for the preparation of polyurethane dispersions is the acetone process.

However, aqueous polyurethane dispersions are becoming more and more important in technical and environmental terms, since they are toxicologically and ecologically safer than polyurethanes in organic solvents.

In principle, most polyurethanes can be converted by means of emulsifiers and extreme shearing forces into aqueous emulsions and dispersions. However, the stability of such emulsions and dispersions is insufficient. For this reason, efforts are being made to develop self-emulsifying polyurethanes which spontaneously form stable dispersions in water without external emulsifiers. For this purpose, in the polymerization of polyurethanes already stabilizing ionic or nonionic molecules are used, which are incorporated into the polymer chain and later serve to stabilize the polyurethane particles in an aqueous environment.

Apart from problems due to undesirable hydrolysis, insufficient hydrophobicity, and reduced stability at high solids contents, it is still difficult to stably disperse crystallization-prone or capable polyurethanes as particles in an aqueous phase. Especially with polyurethanes based on polyester polyols is very difficult to achieve good long-term stability. The particles usually have a very broad particle size distribution and the dispersed polyurethanes do not have particularly high molecular weights.

However, such crystallization of polyurethanes is an important thermo-mechanical property that is desirable in certain applications because temperature control can rapidly and reversibly control physical interactions between the polymer chains. The large increase in viscosity associated with physical crosslinking is particularly important for adhesives.

Thus, there is a need for systems that can stably disperse crystallization-prone polyurethane particles in an aqueous phase, thereby providing particles of significantly narrower size distribution and higher molecular weights despite their hydrophobic nature. Accordingly, the problem underlying the present invention is to provide processes which enable the stable dispersion of even highly hydrophobic polyurethane particles having comparatively high molecular weights in a continuous aqueous phase.

The present invention is based on the knowledge of the inventors that such dispersions can be realized by a specific selection of the polyols used for the preparation of polyurethanes in combination with certain homogenization.

1. (i) Umsetzen einer Mischung, die eine Polyolmischung und mindestens ein organisches Polyisocyanat umfasst, um ein Polyurethan-Präpolymer herzustellen, wobei die Polyolmischung umfasst:
   1. (a) 40-95 Gew.-%, vorzugsweise 50-90 Gew.-%, noch bevorzugter 60-80 Gew.-% mindestens eines Polyesterpolyols, das einen Schmelzpunkt T_m von größer 0°C besitzt;
   2. (b) 0,1-5 Gew.-%, insbesondere 0,5-4 Gew.-%, mindestens eines Polyols, vorzugsweise eines Polyetherpolyols, das mindestens eine ionische oder potentiell ionische hydrophile Gruppe aufweist; und
   3. (c) 0,5-10 Gew.-%, insbesondere 3-5 Gew.-%, mindestens eines nichtionischen Polyetherpolyols, wobei das Polyetherpolyol ein Polyalkylenglykol Homo- oder Copolymer ist, das einen Gehalt von Ethylenoxid Einheiten von unter 50 mol-% aufweist;
      wobei das Polyurethan-Präpolymer weniger als 5 Gew.-% Ethylenoxid-Einheiten enthält; und
2. (ii) Dispergieren des Polyurethan-Präpolymers in eine kontinuierliche wässrige Phase derart, dass eine stabile Emulsion gebildet wird.

In a first aspect, therefore, the present invention is directed to a process for the preparation of an aqueous polyurethane prepolymer dispersion, characterized in that the process comprises:

1. (i) reacting a mixture comprising a polyol mixture and at least one organic polyisocyanate to produce a polyurethane prepolymer, the polyol mixture comprising:
   1. (a) 40-95% by weight, preferably 50-90% by weight, more preferably 60-80% by weight of at least one polyester polyol having a melting point T _m of greater than 0 ° C;
   2. (b) 0.1-5% by weight, especially 0.5-4% by weight, of at least one polyol, preferably a polyether polyol, having at least one ionic or potentially ionic hydrophilic group; and
   3. (c) 0.5-10% by weight, in particular 3-5% by weight, of at least one nonionic polyether polyol, where the polyether polyol is a polyalkylene glycol homo- or copolymer which has a content of ethylene oxide units of less than 50 mol% having;
      wherein the polyurethane prepolymer contains less than 5 weight percent ethylene oxide units; and
2. (ii) dispersing the polyurethane prepolymer into a continuous aqueous phase such that a stable emulsion is formed.

In various embodiments, in a next step, the polyurethane prepolymer is reacted with a suitable chain extender to form an aqueous polyurethane dispersion form. In a further aspect, therefore, the invention relates to processes for preparing an aqueous polyurethane dispersion (PUD), characterized in that the polyurethane prepolymer is reacted in the aqueous polyurethane prepolymer dispersion with a suitable chain extender to an aqueous polyurethane dispersion form.

In further aspects, the invention is directed to the thus obtainable polyurethane prepolymer dispersions and polyurethane dispersions.

Still other aspects of the invention relate to compositions containing the polyurethane dispersions described herein, especially adhesive compositions or coating compositions.

Finally, the invention is also directed to the use of a polyurethane dispersion as obtainable by the methods described herein as an adhesive, coating or rheology modifier.

The present invention is directed to a process for preparing stable polyurethane dispersions which process employs certain amounts of ionic and nonionic groups which are incorporated into the polyurethane prepolymers during polymerization and impart the desired improved stability to them. Surprisingly, the inventors have found that the use of only minor amounts of nonionic polyethylene glycol and instead the use of more hydrophobic polyalkylene glycols, such as, in particular, polypropylene glycol, results in a narrower particle size distribution of the dispersed particles. Furthermore, such polypropylene glycol units are better suited than the corresponding polyethylene glycols to stabilize polyurethane polymers containing groups or units prone to crystallization in aqueous dispersions. To stabilize such polyurethanes containing high melting point polyol units, it is further advantageous to minimize the amount of ionic groups. It is believed, inter alia, that a high proportion of ionic groups or polyethylene glycol units results in a phase separation within the polymer particles between a phase rich in the more hydrophilic portions, such as the ionic groups and the hydrophilic polyether units, and a Phase, which is rich in crystallization-prone hydrophobic polyester, comes, but is undesirable because it negatively affected the crystallization kinetics and thus the particle stability. This can be explained by the fact that such a phase separation reduces the local concentration of non-crystallisable polymer segments. This in turn leads to a reduction in crystallization inhibition by these noncrystallizable polymer segments which interfere with nucleation and crystallite growth, ie, the likelihood of crystallite formation in the polymer particles increases. It is believed that this behavior also the explanation for the higher stability of homogeneous particles is that the formation of crystallites influences the colloidal stability by interrupting the isotropic stabilization of the formed crystallites at the surface of the particle at the corresponding position.

The reduction in the proportion of hydrophilic and in particular ionic groups is also advantageous because it reduces the tendency of adhesives and coatings produced from the polyurethane dispersions to absorb water and thus counteracts a deterioration of the mechanical properties.

The polyurethane prepolymers described herein are therefore characterized by containing ionic and certain non-ionic, non-crystallizable polymer segments which are sufficient for stable dispersion in aqueous phases but at the same time inhibit crystallization by the non-ionic, non-crystallizable polymer segments used are compatible with the crystallization-prone polyester segments so that a homogeneous particle can be formed.

In various embodiments of the processes described herein, the polyurethane prepolymers are synthesized from a mixture of polyols having the desired properties and suitable polyisocyanates, especially diisocyanates that link the polyols together. It is obvious to a person skilled in the art that this approach can also be carried out in reverse, i. a mixture of polyisocyanates having the desired properties can be reacted with corresponding polyols / diols as a linking reagent. In the following, the detailed approach of the invention refers to the former approach, it being understood by those skilled in the art that the following description, with appropriate modifications, is also applicable to a process employing a mixture of polyisocyanates as the starting material.

The polymer segments of the polyurethanes which tend to crystallize and are used according to the invention are preferably polyester polyols. In particular, those polyester polyols are preferred whose melting point T _{m is} greater than 0 ° C, preferably greater than 40 ° C. In further embodiments, the melting point T _m <100 ° C, preferably <80 ° C. The indication of the melting point refers to the melting point of corresponding high molecular weight, linear polyester homopolymers. Methods suitable for determining melting points are known in the art. Particularly suitable is the determination by differential calorimetry (DSC = differential scanning calorimetry) according to ISO11357.

The polyesters used are preferably polyols, i. have free hydroxyl groups. In particular, they are polyester diols, i. (preferably linear) polyesters having two terminal hydroxyl groups.

Suitable polyesters can be prepared by known processes, for example condensation reactions, from polyols and polyacids, in particular from diols and diacids. Particularly suitable diols are aliphatic alkanediols, such as ethanediol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, and mixtures thereof. In principle, the use of cyclic diols or aromatic diols is conceivable, but preference is given to the use of linear aliphatic diols, such as those mentioned above, in particular of 1,2-propanediol, 1,3-propanediol, 1,4-butanediol and 1,6- Hexanediol, most preferably 1,4-butanediol. The diacids used are above all dicarboxylic acids and here preferably linear aliphatic dicarboxylic acids. Examples of suitable acids include, but are not limited to, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, and mixtures thereof. Again, it is in principle possible to use cyclic or aromatic dicarboxylic acids such as phthalic acid, terephthalic acid or isophthalic acid, however, the resulting polyesters have significantly increased melting and glass transition temperatures compared to those produced with aliphatic dicarboxylic acids. A particularly preferably used polyester is poly (tetramethylene adipate) (PTMA), which can be prepared by a condensation reaction of 1,4-butanediol and adipic acid.

Alternatively, suitable polyesters may also be synthesized from cyclic esters, especially lactones, or hydroxycarboxylic acids. A particularly preferred ester used here is ε-caprolactone, the lactone of the ω-hydroxycaproic acid, the polyester from which can be represented by ring-opening polymerization.

The polyester polyols used to form the polyurethane prepolymers usually have an average molecular weight M _n of 500 to 5000, preferably 1000-4000 and particularly preferably 2000 to 3500 g / mol

The polyester polyols are used in the polyol mixtures in amounts of 40 to 95 wt .-%, preferably 50-90 wt .-%, in particular 60-80 wt .-% each based on the polyol mixture. At amounts greater than 95 wt .-%, possibly even greater than 90 or even greater than 80 wt .-%, the total content of hydrophilic groups may be too low, which may adversely affect the stability. At levels below 40% by weight, the particles no longer have the desired physical properties.

Unless otherwise stated, where molecular weights are referred to in the present application, the numbers are based on the number average molecular weight (M _n ). The molecular weight M _n can be determined on the basis of an end group analysis (hydroxyl number according to DIN 53240-1: 2013-06 / isocyanate content according to Spiegelberger according to EN ISO 11909: 2007-05), or by gel permeation chromatography (GPC) according to DIN 55672-1: 2007-08 THF be determined as eluent. Unless otherwise stated, the number average molecular weights reported were determined by end group analysis. In addition, the weight-average molecular weight M _{w can be determined} by GPC as indicated above for M _n .

"At least one" as used herein means 1 or more, i. 1, 2, 3, 4, 5, 6, 7, 8, 9 or more. With respect to an ingredient, the indication refers to the type of ingredient, not the absolute number of molecules. "At least one polyester polyol" thus means at least one type of polyester polyol, i. that one type of polyester polyol or a mixture of several different polyester polyols can be used. The term, together with weights, refers to all compounds of the type indicated which are included in the composition / mixture, i. that the composition does not contain any further compounds of this type beyond the stated amount of the corresponding compounds.

All percentages given in connection with the compositions described herein, unless explicitly stated otherwise, relate to% by weight, in each case based on the mixture in question.

The polyols used herein having at least one ionic or potentially ionic hydrophilic group are preferably compounds having anionic or potentially anionic groups. Examples of such compounds are polyether polyols which have at least one, preferably per molecule, exactly one anionic or potentially anionic hydrophilic group.

Generally, as ionic groups are, but are not limited to, sulfate, sulfonate, phosphate, phosphonate, carboxylate, and ammonium groups, as well as ionic heterocycles, especially nitrogen-containing, 5-6 membered heterocycles. Potentially ionic groups include, but are not limited to, those selected from the group consisting of carboxylic acid and amino groups as well as uncharged heterocycles, especially nitrogen-containing, 5-6 membered heterocycles. "Potentially ionic" herein refers to the property of being present in an aqueous environment at the appropriate pH as an ionic compound. Polyols containing such ionic or potentially ionic groups are described, for example, in US Pat US 3,756,992 . US 3,479,310 and US 4,108,814 described.

Very particular preference is given to sulfonate groups. Sulfonate-containing diols are described, for example, in DE 2446440 and DE 2437218 described. Preference according to the invention is given to polyether polyols, in particular those based on propylene glycol, which contain at least one sulfonate group. Suitable is, for example, an alkoxylated, in particular propoxylated, adduct of an alkenediol, in particular 2-butene-1,4-diol, and a sulfite, in particular a hydrogen sulfite, such as NaHSO ₃ .

The (potentially) ionic polyols used herein in various embodiments have an average molecular weight M _n in the range of 200 to 1000, preferably 300 to 500 g / mol. Particularly preferred is an alkoxylated, in particular propoxylated, adduct of an alkenediol, in particular 2-butene-1,4-diol, and a sulfite, in particular a hydrogen sulfite, such as NaHSO ₃ , having a molecular weight M _n of about 430.

The (potentially) ionic polyols, in particular anionic polyether polyols, are used in the polyol mixtures in amounts of from 0.1 to 5% by weight, in particular 0.5-4% by weight, based in each case on the polyol mixture. For amounts less than 0.1 wt .-%, possibly even less than 1 wt .-%, the hydrophilicity may be too low to allow a stable dispersion, with amounts greater than 5 wt .-% outweigh the adverse effects on the Stabilization due to phase separation within the particles (microphase separation in the particles). It is generally advantageous that the (potentially) ionic polyols used, in particular anionic polyols, have a sufficient solubility in the polyols without having to additionally employ solubility promoters. In particular, the use of pyrrolidones such as NMP ( N- methylpyrrolidone) or NEP ( N- ethylpyrrolidone) and other aprotic solvents, such as without limitation DMSO or DMF, as solubility promoters should - if possible - be avoided by choosing a suitable ionic polyol of sufficient solubility , In a particularly preferred embodiment, therefore, propoxylated or butoxylated ionic polyols are used which carry quasi propylene oxide or butylene oxide repeating units as internal solubility promoters in the molecule.

The (potential) ionic polyols are preferably used in amounts which are such that the content of ionic groups in the polyurethane prepolymer is not more than 20 milliequivalents, preferably not more than 10 milliequivalents per 100 g prepolymer.

The nonionic polyether polyols used in the polyol mixture are preferably those which are not crystallizing, ie are not capable of crystal formation. Various embodiments are polylalkylene glycols, with the exception of polyethylene glycol, for example, polypropylene glycol, polybutylene glycol, poly (neo) pentylene glycol, or copolymer the said one another or else with polyethylene oxide, the content of polyethylene oxide in the corresponding polyol being less than 50% by weight, preferably less than 45% by weight, more preferably less than 10% by weight. In various embodiments, the HLB value after Griffin (HLB = Hydrophilic-Lipophilic Balance) of these nonionic polyalkylene glycols is <10, preferably <6 and more preferably ≦ 3. Particularly preferred is a polypropylene glycol homopolymer or a polypropylene glycol / polyethylene glycol block copolymer, preferably with an ethylene oxide content of 45 mol% or less, more preferably 10% or less.

The nonionic polyether polyols used herein in various embodiments have an average molecular weight M _n in the range of 1000 to 4000, preferably 1500 to 2500 g / mol.

The nonionic polyether polyols are used in the polyol mixtures in amounts of from 0.5 to 10% by weight, in particular from 3 to 5% by weight, based in each case on the polyol mixture.

The inventors have surprisingly found that the use of the abovementioned nonionic polyether polyols instead of the hitherto commonly used hydrophilic polyether polyols, which consist predominantly of polyethylene glycol, although larger particle sizes but also provide much narrower particle size distributions. In addition, the poor long-term stability of polyethylene glycol-rich polyether polyols, which tend to coagulate after several days or weeks, is markedly improved by the use of the polyols described herein. Without wishing to be bound by any particular theory, it is believed that in a conventional dispersion, the polyethylene glycol-rich segments migrate to the interface of the particles (ie towards the water phase), while the crystallizable polyester segments accumulate in the core accordingly. As soon as crystallization begins, the dispersions become unstable. With less polyethylene glycol or more polypropylene glycol, there is no such phase separation in the particle, the polyester segments in the interior of the particles are "diluted" by polypropylene glycol segments and additionally disturbed in their crystallization, so that the particles remain stably dispersed.

In various embodiments of the processes described herein, the polyurethane prepolymer has an average molecular weight in the range of 3000-15000, especially 5000 to 10000 g / mol. The desired molecular weights are set by the use of appropriate amounts of polyols and polyisocyanates and determined by means of suitable measuring methods, such as end group analysis (hydroxyl number according to DIN 53240-1: 2013-06 or isocyanate content according to Spielberger according to EN ISO 11909: 2007-05). Corresponding calculations and methods are readily known to the person skilled in the art.

As already described above, the content of ionic groups in the polyurethane prepolymer is preferably at most 20 milliequivalents, preferably at most 10 milliequivalents per 100 g prepolymer.

The prepolymer contains less than 5 weight percent ethylene oxide units, i. the polyurethane prepolymer synthesized by the methods described herein contains less than 5% by weight of EO units based on its total weight.

It is further preferred to use the organic polyisocyanate in molar excess relative to the polyol mixture to obtain an NCO-functionalized polyurethane prepolymer. When the polyisocyanates are used in molar excess, the OH / NCO equivalent ratio is preferably 1: 1.1 to 1: 4, more preferably 1: 1.2 to 1: 1.3.

The organic polyisocyanate is a compound having at least two isocyanate groups (-NCO), especially a diisocyanate. However, under certain circumstances, it may be advantageous to employ small amounts of isocyanates having a functionality greater than 2. In such cases, polyisocyanates based on hexamethylene diisocyanate or polymeric diphenylmethane diisocyanate are used in particular. Suitable polyisocyanates include, but are not limited to, aromatic diisocyanates such as diphenylmethane diisocyanate (MDI), polymeric MDI (PMDI), and / or toluene diisocyanate (TDI), and aliphatic diisocyanates such as hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and / or methylene-4,4-bis (cyclohexyl) diisocyanate (H12MDI), or mixtures thereof. Although both aromatic and aliphatic polyisocyanates can be used, aliphatic polyisocyanates, especially diisocyanates, such as IPDI and HDI, are preferred according to the invention.

To form the prepolymer, the polyols and the polyisocyanates are preferably mixed, whereby the mixture can be heated. This may be particularly necessary if the polyols used are solid at room temperature and must be melted to form the polyol mixture. In preferred embodiments, the polyols are combined and heated with stirring and vacuum to about 70 to 95 ° C, for example about 75 ° C, to melt and optionally dry. The prepolymer synthesis is usually carried out by adding the isocyanates and at elevated temperature, in particular at a temperature which is greater than the melting point T _{m of} the polyester polyols, preferably in the range between 70 and 95 ° C, over a period of about 1 to about 5 hours, preferably about 2-3 hours. The reaction is typically carried out in the presence of a catalyst which is added, preferably a bismuth, tin, zinc or titanium based catalyst, more preferably Bismuth (III) neodecanoate, zinc (II) neodecanoate, zinc (II) 2-ethylhexanoate, dibutyltin dilaurate (DBTDL) or dimethyltin dineodecanoate, the latter being commercially available, for example, as Fomrez UL-28. Alternatively, the catalysis can also be carried out as metal-free acidic or basic catalysis.

The reaction is carried out until the free isocyanate content is near the calculated value, as determined by standard titration with dibutylamine. Preferred values for the free isocyanate content are in the range of 0.2 to 2% by weight, preferably 0.7 to 1.8% by weight relative to the total amount of polyol and polyisocyanate in the mixture. Once the desired value is reached, the temperature is reduced, for example to 60 ° C.

"Approximately" as used herein in reference to numerical references refers to ± 10%, preferably ± 5% of the numerical value to which the claim refers. Thus, "about 70 ° C" means 70 ± 7, preferably 70 ± 3.5 ° C.

As already mentioned above, the isocyanate is preferably used in molar excess based on the stoichiometric concentration required to completely react all hydroxyl groups. The excess may be an OH / NCO equivalent ratio of 1: 1.1 to 1: 4. Preferably, the amount of polyisocyanate used is 20% to 150% greater than the stoichiometric concentration required to react all the hydroxyl groups.

The prepolymer formed can be used either as such, but preferably in the form of a solution in a suitable organic solvent, preferably a water-miscible, -NCO group inert organic solvent, including but not limited to acetone, ethyl acetate and N-methylpyrrolidone.

To form the dispersion of the polyurethane prepolymer, the formed prepolymer or its solution is dispersed or emulsified in a continuous aqueous phase, usually water or an aqueous solution.

To form the emulsion / dispersion, it is possible to use mechanical stirrers or rotor-stator mixers, for example an Ultra-Turrax apparatus, as well as homogenizers or ultrasound machines.

The dispersing or emulsifying step may generally be carried out at elevated temperature, for example in the range of 30-60, for example about 40 ° C.

In various embodiments, a preemulsion may first be formed, which is then homogenized in a subsequent step by a suitable method, for example, a high shear method, to form an emulsion.

"Emulsion" as used herein refers to an oil-in-water (O / W) emulsion in which the emulsified phase is in the form of droplets or particles, preferably of approximately spherical shape, in the continuous water phase. In this case, the droplets / particles have an average size, in an approximately spherical shape an average diameter, in the size range of 30 to 1000 nm, in particular 50 to 500 nm, particularly preferably 100 to 300 nm. The above-mentioned averaged values refer to the z -Means ("z-average") from dynamic light scattering according to ISO 22412: 2008.

1. (a) Emulgieren einer Lösung des Polyurethan-Präpolymers in einem geeigneten Lösungsmittel eine kontinuierliche wässrige Phase, insbesondere Wasser, um eine Präemulsion zu bilden; und
2. (b) Homogenisieren der Präemulsion und optional Entfernen des Lösungsmittels, vorzugsweise mittels Destillation, um eine stabile Emulsion zu bilden.

Step (ii) of the method described herein therefore comprises the steps in various embodiments:

1. (a) emulsifying a solution of the polyurethane prepolymer in a suitable solvent, a continuous aqueous phase, especially water, to form a preemulsion; and
2. (b) homogenizing the pre-emulsion and optionally removing the solvent, preferably by distillation, to form a stable emulsion.

This step can be modified accordingly when using the prepolymer as such. In particular, the prepolymer is then dispersed directly into the continuous phase and then homogenized.

To form the preemulsion, mechanical stirrers or rotor-stator mixers, for example an Ultra-Turrax apparatus, can be used, to form the emulsion preferably a homogenizer, for example a microfluidizer (as available from Microfluidics), or an ultrasound machine is used ,

As already described, the dispersion step, in particular the homogenization step, can be carried out by means of a high shear process. Suitable high shear methods preferably have shear rates of at least 1,000,000 / s and / or an energy input per time of at least 10 ⁶ J / s * m ³ . The shear rate can be calculated by means known in the art or is known for given devices. In general, the shear rate is calculated from the ratio of the maximum flow velocity (V _max ) of a substance, for example a liquid in a capillary, and the radius of the hollow body through which it flows. The energy input per time results from the energy density in J / m ³ per time.

The aqueous polyurethane dispersion is then formed from the emulsion of the prepolymer. For this purpose, a suitable chain extender is added to the emulsion and reacted with the prepolymer. Suitable chain extenders are generally compounds which have at least two groups which are reactive with the end groups of the prepolymer, usually -NCO groups. Examples of chain extenders containing at least two terminal NCO-reactive groups include, but are not limited to, diamines such as hydrazine, an alkylenediamine or cycloalkylenediamine, preferably ethylenediamine, isophoronediamine, piperazine, or polyetheramine, and diols such as butanediol or 2-butyl-2-ethyl-1,3-propanediol. The chain extension reaction can be carried out until complete conversion of the isocyanate groups, i. the chain extender is added continuously until no more free isocyanate groups are detectable. For the chain extension reaction, the presence of a catalyst or an elevated temperature may be required.

As already mentioned above, the invention also relates to the dispersions prepared by the processes described herein or the corresponding polyurethane (pre) polymers. The dispersions in various embodiments may have solids contents in the range of from 10 to 60 wt%, preferably about 15 to 50 wt%, more preferably about 20 to 50 wt%.

The polyurethane dispersions can be used, for example, in adhesive or coating compositions. Other applications include sealants, fiber sizes, rheology modifiers, paints, detergents and cosmetics. Accordingly, the invention is also directed to corresponding compositions containing the dispersions of the invention. Such compositions may contain other ingredients as are conventional and known in the art.

When used as adhesives or coating compositions, the boundary phases of (partially) crosslinked particles constitute mechanical weak points in the polymer films, which are subsequently reinforced for many applications. For example, in the case of dispersion-based adhesives and coatings, post-crosslinking of the dried polymer films is usual. For the inter-particle crosslinking of films of polyurethane dispersions, various systems have been described in the prior art which the person skilled in the art can select and apply on the basis of his specialist knowledge.

Adhesive compositions containing the polyurethane dispersions of the invention may therefore, for example, contain at least one external crosslinker in various embodiments of the invention. The term "external crosslinker" as used herein a compound which is not bound to the polyurethane before the crosslinking reaction but is dissolved or dispersed in the polyurethane dispersion. Suitable external crosslinking agents are, for. As polyisocyanates having at least two isocyanate groups, for. B. isocyanurates formed from diisocyanates, compounds having at least one carbodiimide group (especially when the polyurethane contains carboxyl groups), chemically blocked isocyanates or encapsulated isocyanates (especially in 1K systems), encapsulated uretdiones, biurets or allophanates. Also suitable are aziridines, oxazolines and epoxides. For example, aliphatic polyisocyanates, in particular water-emulsifiable polyisocyanates, for. B. Basonat® LR9056 can be used. The postcrosslinker systems described above are described in detail in the patent publications WO 2000/037526 A1 . EP 1 600 485 A1 . EP 0 436 941 A1 . US 4,190,567 A . DE 35 238 56 A1 and US 5,133,997 A as well as the publications Meier-Westhues, U. (Polyurethanes: Coatings, Adhesives and Sealants, 2nd edition; Vincentz 2007 ) Wicks & Wicks (Blocked isocyanates III: Part A. Mechanisms and chemistry, Prog. Org. Coat., 1999, 36 (3), 148-172 ) and Müller & Poth (paint formulation and paint formulation, 3rd edition, Vincentz 2009 ).

The external crosslinker is preferably used in an amount of 0.5 to 10 wt .-%, based on solids content of the dispersion.

In various embodiments, the polyurethane may already carry uretdione units introduced in the preparation of the prepolymers. These can then react with the crosslinking with amines (preferably surface-deactivated, solid (meltable) polyamines in powder form). Such systems are for example in the international patent publication WO 2012/130711 described.

However, in other embodiments, the adhesive compositions may also contain crosslinkers that are attached to the polyurethane (internal crosslinkers).

With chemical post-crosslinking, the mechanical strengths of the polymer films produced can be drastically increased.

The polyurethane dispersions described herein can be used, for example, in aqueous adhesive formulations for the production of laminates, ie in aqueous laminating adhesive formulations for bonding large-area substrates, in particular for the production of composite films. In such methods of making composite films, at least two substrates are adhered together using the aqueous polymer dispersion. The substrates are typically large area, flexible components, of which at least one, preferably two, are polymeric films.

The present invention thus also relates to a process for producing composite films in which an aqueous polyurethane dispersion described above is used. Here, the aqueous polymer dispersions can be used as such or after preparation with conventional excipients as aqueous adhesive formulations. Usual auxiliaries are, for example, wetting agents, thickeners, protective colloids, light stabilizers, biocides, defoamers, etc. In such processes, the optionally prepared polyurethane dispersion is applied, for example, to a plastic or metal foil and combined with one or more further plastic and / or metal foils to form a composite foil bonded.

The adhesive formulations according to the invention do not require additions of plasticizing resins (tackifiers) or other plasticizers in various embodiments.

In the described method for the production of composite films, in various embodiments, the inventive polymer dispersion or a correspondingly prepared preparation on the substrates to be bonded preferably with a layer thickness of 0.1 to 20 g / m (2), more preferably 1 to 7 g / m (2) z. B. by doctoring, brushing, etc. applied. It can be applied to conventional coating methods, for. Roll coating, counter roll coating, gravure roll coating, countergraduate roll coating, brush coating, bar brushing, spray coating, airbrush coating, meniscus coating, curtain coating or dip coating. After a short time to vent the dispersion water (preferably after 1 to 60 seconds), the coated substrate can then be laminated with a second substrate, wherein the temperature z. B. 20 to 200 ° C, preferably 20 to 100 ° C and the pressure z. B. 100 to 3000 kN / m ² , preferably 300 to 2000 kN / m ² may be.

All documents cited are incorporated herein by reference in their entirety.

The following examples are given to illustrate the invention, but the invention is not limited thereto.

Examples example 1 Polyurethane synthesis:

Before the reaction, the polyols used, with the exception of 1,4-butanediol at 70-80 ° C in a vacuum (<1mbar) dehydrated. All reactions were carried out under nitrogen atmosphere. The syntheses were carried out in a four-necked round bottom flask equipped with thermometer, Schlifffolive for nitrogen inlet, KPG stirrer and reflux condenser with attached drying tube. The synthesis was carried out at 70.degree.

The following educt mixtures were used: PUA PU B PU C PU D PU E Adipic acid-butylene glycol polyester (M _n 3200) 79.80 g 79.80 g 79.80 g 375.55 g 278.70 g Adipic acid-butylene glycol polyester (M _n 2015) 10,20 g 10,20 g 10,20 g 50.70 g 37.70 g Sulfonated Diol (M _n 430) 5.00 g 5.00 g 5.00 g - - EO / PO copolymer (Konion DR-802 from Green Soft Chem, M _n 2000, EO / PO = about 8/2) 10.00 g 5.00 g - - - EO-PO-EO block copolymer (Tergitol L61 PU from Dow, M _n 2000, EO / PO = approx. 1/9) - 5.00 g 10.00 g - 103.9 g EO / PO copolymer (Synalox 40-D300 from Dow, M _n 3500, EO / PO = 6/4) - - - 15.00 g - 1,4-butanediol - - - 1.01 g 0.738 g isophorone 15.19 g 15.19 g 15.19 g 55.06 g 48.59 g Formrez UL-28 solution in acetone (50% by weight) 12 mg 12 mg 12 mg 50 mg 50 mg

The prepolymers synthesized in this way were capped with 5.62 g of dibutylamine for further investigations after reaching the theoretical NCO value.

Preparation of the emulsions:

The emulsions were prepared by first disperse and continuous phase separately prepared and mixed. These were then mixed together and first pretreated with an Ultra-Turrax rod (1-3 min at 11k rpm) to produce a pre-emulsion. Subsequently, the mini-emulsification was carried out with a high-pressure homogenizer of Microfluidics (3 passes). For the preparation of the emulsions, 11.5 g of the prepolymers PU A, PU B and PU C were each dissolved in 11.5 of ethyl acetate and miniemulgiert in 75 g of water.

DLS measurements:

DLS measurements of the prepared emulsions directly after homogenization gave the following values: sample z-average (DLS) / nm Normalized standard deviation (DLS) /% PUA 141 25 PU B 189 20 PUC 235 10

Example 2 Polyurethane synthesis:

The synthesis was carried out in a suitable 4 necked flask with reflux condenser, KPG stirring shaft, N ₂ inlet and internal contact thermometer. The polyols were melted and dehydrated at 75 ° C and 1 mbar. Thereafter, work continued under an N ₂ protective atmosphere. Isophorone diisocyanate and then hexamethylene diisocyanate were added to this mixture at 70.degree. After addition of Formrez UL 28 (50 wt.% In acetone), the resulting exotherm was intercepted by cooling with an ice bath until the mixture did not become warmer than 85 ° C. When the exotherm subsided, the temperature was held at 85 ° C for an additional hour. Subsequently, the proportion of isocyanate groups was titrated according to Spielberger. When the desired isocyanate content had been reached, the prepolymer was cooled to about 50 ° C. and dissolved in 150 g of molecular sieve (3 Å) of dried acetone.

Production methods of the emulsions:

Without homogenizer: To the prepolymer dissolved in acetone 150 g of demineralized water were added within 5 minutes. This resulted in a white emulsion. From this emulsion, the solids content was measured. To the emulsion, an aqueous solution of isophoronediamine (70 mol% of amine relative to NCO) was added dropwise with stirring (250 rpm). Subsequently, the solids content was determined again. From the emulsion, the acetone was distilled off in a rotary evaporator. Thereafter, DLS and solid content were measured.

Preparation of the emulsion with the homogenizer: The prepolymer dissolved in acetone was pre-emulsified in water at 40 ° C. within 5 minutes with Ultra-Turrax T25 basic at 11000 rpm. This pre-emulsion was then applied to the homogenizer (Microfluidizer M-100Y from Microfluidics) at 40 ° C. in 4 passes (1st chamber: H210Z 200 μm, 2nd chamber: H230Z 400 μm. 700 bar). From this emulsion, the solids content was measured. To the emulsion, an aqueous solution of isophoronediamine (70 mol% of amine relative to NCO) was added dropwise with stirring (250 rpm). Subsequently, the solids content was determined again. From the emulsion, the acetone was distilled off in a rotary evaporator. Thereafter, DLS and solid content were measured.

polyurethanes:

specification PU 1 PU 2 PU 3 PU 4 M _n prepolymer (g / mol) 5000 7000 9000 12000 Amount / g PU 1 PU 2 PU 3 PU 4 K320 (Hosung Chemex Co., Ltd.) 117.74 117.85 118.72 158.28 DR-802 (KPX Green Chemical) 3.00 4.50 4.50 6.00 Tergitol L-61 PU Surfactant (Dow Europe Gmbh) 6.00 6.00 6.00 8.00 GS-7Q (Yedang G & B Co., Ltd.) 3.00 3.00 3.00 4.00 Isophorone diisocyanate (Merck) 15,30 14.09 13.42 21.88 1,6-hexamethylene diisocyanate 4.96 4.57 4.35 1.84 Formrez UL 28 (Momentive Amer Ind.) 0,035 0,035 0,035 0,040 Total mass (g) 150.04 150.05 149.99 200.04

After 1 hour at 85 ° C, an NCO content of 1.80 wt .-% (PU 1), 1.33 wt .-% (PU 2), 1.06 wt .-% (PU 3) and 0 , 77 wt .-% (PU 4) determined.

Emulsification without high shear procedure:

• 150.0 g of the prepolymer PU 1 / acetone mixture were emulsified with 150.0 g of demineralized water.
• After emulsification, a solids content of 25.2% was determined.
• 50.0 g of the prepolymer PU 2 / acetone mixture were emulsified with 50.0 g of demineralized water.
• After emulsification, a solids content of 25.6% was determined.
• 150.0 g of the prepolymer PU 3 / acetone mixture were emulsified with 150.0 g of demineralized water.
• After emulsification, a solids content of 21.5% was determined.
• Emulsification of the prepolymer PU 4 was not possible. The addition of water did not produce a stable emulsion. The product was creamy and dilution with water was not possible.

Chain extension:

The chain extension of PU 1 was carried out with 3.8 g of isophoronediamine in 10 g of deionized water. Thereafter, a solids content of 27.2% was determined.

The chain extension of PU 2 was carried out with 0.9 g of isophoronediamine in 5 g of deionized water. Thereafter, a solids content of 25.5% was determined.

The chain extension of PU 3 was carried out with 2.3 g of isophoronediamine in 10 g of deionized water. Thereafter, a solids content of 20.8% was determined.

After rotating the emulsion, the following measured values were obtained: Used PU PU 1 PU 2 PU 3 Solids content: 32.3% 35.7% 39.6% particle size Average diameter z-average 325 nm 540 nm 296 nm standard. standard deviation 0.22 0.57 0.19

Preparation of the emulsion with the homogenizer:

• 81.3 g of the prepolymer PU 1 / acetone mixture were emulsified with 60.0 g of demineralized water.
• After emulsification, a solids content of 27.9% was determined.
• 80.9 g of the prepolymer PU 2 / acetone mixture were emulsified with 60.0 g of demineralized water.
• After emulsification, a solids content of 25.1% was determined.
• 81.0 g of the prepolymer PU 3 / acetone mixture were emulsified with 60.0 g of demineralized water.
• After emulsification, a solids content of 24.6% was determined.
• 80.21 g of the prepolymer PU 4 / acetone mixture were emulsified with 60.00 g of demineralized water.
• After emulsification, a solids content of 27.6% was determined.

Chain extension:

• The chain extension of PU 1 was carried out with 2.1 g of isophoronediamine in 10 g of deionized water. This resulted in a solids content of 26.0%.
• The chain extension of PU 2 was carried out with 1.7 g of isophoronediamine in 10 g of deionized water. Thereafter, there was a solids content of 23.5%.
• The chain extension of PU 3 was carried out with 1.2 g of isophoronediamine in 10 g of deionized water. This resulted in a solids content of 23.6%.
• The chain extension of PU 4 was carried out with 0.9 g of isophoronediamine in 10 g of deionized water. This resulted in a solids content of 26.6%.

After rotating the emulsion, the following measured values were obtained: Used PU PU 1 PU 2 PU 3 PU 4 Solids content: 35.5% 38.6% 32.2% 36.4% particle size Average diameter z-average 250 nm 211 nm 198 nm 490.1 nm standard. standard deviation 0.22 0.16 0.23 0.23

Example 3

The polyurethane prepolymers were prepared analogously to the previous example. The synthesis temperature was about 80 ° C. PU A PU B PU C PU D Realkyd XTR 30110 (Arkema) / g 373.89 374.12 374.34 374.12 K-HN-8200 (polyether, Mn about 2000 g / mol, 80% EO, Hannong Chemicals) / g 40,00 20.00 - - Tergitol L-61 (polyether, Mn about 2000 g / mol, 10% EO, Dow Chemical) / g - 20.00 40,00 - Voranol 2000L (Dow Chemical) / g - - - 40,00 GS-7Q (Yedang G & B Co., Ltd.) / g 20.00 20.00 20.00 20.00 Isophorone diisocyanate (Merck) / g 66.11 65.90 65.66 65.88 Fomrez UL 28 (50% by weight in acetone) / g 0.10 0.10 0.10 0.10 Dibutylamine / g 17.90 18.18 15.00 17.80

Subsequently, the prepolymers were dissolved 1: 1 in ethyl acetate and end-capped with dibutylamine. The polyurethane solutions were emulsified in water as in the previous example with a homogenizer. Their colloidal properties were as follows (the EO content refers to the nonionic polyether polyols). sample PU EO salary /% z-average / nm normalized standard deviation ME A PUA 80 135 0.26 ME B PU B 45 173 0.22 ME C PU C 10 222 0.17 ME D PU D 0 275 0.06

The particle size distribution of the emulsions is in FIG. 1 shown.

Highly diluted emulsions were dried on silicon wafers and analyzed by SEM. The pictures are in FIG. 2 shown, wherein in the samples A and B shows a phase separation in the particles.

Dispersions C and D proved to be stable for over 6 months; Emulsions 3A and 3B precipitated over 2 months. To further investigate the colloidal stability, the emulsions were reproduced and the solids content was recovered by distillation of water 40 wt .-% increased. In emulsion A, a coagulum swollen with water formed at elevated solids content, which proved to be partially crystalline (DSC).

Example 4

The prepolymer synthesis was carried out analogously to the previous examples.

The addition of the catalyst was carried out here in two steps. 50 μL of the solution was added to start the reaction, another 40 μL after the exotherm had ceased. The synthesis was carried out at about 70 ° C. Before emulsification, the prepolymer was dissolved in acetone. Realkyd XTR 30110 (Arkema) / g 750.15 K-HN-8200 (polyether, Mn about 2000 g / mol, 80% EO, Hannong Chemicals) / g 40,00 Tergitol L-61 (polyether, Mn about 2000 g / mol, 10% EO, Dow Chemical) / g 40,00 GS-7Q (Yedang G & B Co., Ltd.) / g 40,00 Isophorone diisocyanate (Merck) / g 129.85 Fomrez UL 28 (50% by weight in acetone) / μL 90

The dispersion was carried out analogously to the previous batch with Ultraturrax mixer and homogenizer. The prepolymer dispersion was divided and mixed with 0-120 mol% of the diamines ethylenediamine (EDA), isophoronediamine (IPDA) and piperazine (each as an aqueous solution). The stated amount of diamine is given here relative to the polyurethane prepolymers. All dispersions remained colloidally stable, no particle size changes (DLS) and no coagulum were observed: sample z-average / nm PDI before chain extension 164 0.02 120 mol% piperazine 178 0.12 120 mol% EDA 176 0.04 120 mol% IPDA 169 0.02

By gel permeation chromatography, the apparent molecular weights (against polystyrene standards) of the dried polymers were determined. The following table shows the molecular weights for different amounts of chain extenders. For reference a portion of the prepolymer dispersion was reacted with a slight excess of dibutylamine, in which case an M _w of 22800 g / mol was measured. Amount chain extender M _w with EDA / kg / mol M _w with piperazine / kg / mol M _w with IPDA / kg / mol 0 mol% 115 115 115 10 mol% 96 118 104 20 mol% 110 115 109 30 mol% 120 115 117 40 mol% 114 117 123 50 mol% 120 121 124 55 mol% 127 124 131 60 mol% 123 119 133 65 mol% 129 120 134 70 mol% 136 124 145 75 mol% 144 125 148 80 mol% 136 124 140 85 mol% 131 122 117 90 mol% 137 129 103 95 mol% 142 131 92 100 mol% 142 123 81 120 mol% 134 134 58

Claims (15)

A process for preparing an aqueous polyurethane prepolymer dispersion, characterized in that the process comprises: (i) reacting a mixture comprising a polyol mixture and at least one organic polyisocyanate to produce a polyurethane prepolymer, the polyol mixture comprising: (a) 40-95 wt .-%, preferably 50-90 wt .-%, more preferably 60-80 wt .-% of at least one polyester polyol having a melting point T _m of greater than 0 ° C; (b) 0.1-5% by weight, especially 0.5-4% by weight, of at least one polyol, preferably a polyether polyol, having at least one ionic or potentially ionic hydrophilic group; and (c) 0.5-10% by weight, in particular 3-5% by weight, of at least one nonionic polyether polyol, where the polyether polyol is a polyalkylene glycol homo- or copolymer which has a content of ethylene oxide units of less than 50 mol% having;
wherein the polyurethane prepolymer contains less than 5 weight percent ethylene oxide units; and (ii) dispersing the polyurethane prepolymer into a continuous aqueous phase such that a stable emulsion of the polyurethane prepolymer is formed. The method of claim 1, characterized in that step (ii) comprises: (a) emulsifying a solution of the polyurethane prepolymer in a suitable solvent into a continuous aqueous phase, especially water, to form a preemulsion; and (b) homogenizing the pre-emulsion and optionally removing the solvent to form a stable emulsion. The method of claim 1 or 2, characterized in that the polyester polyol (i) is a polyester polyol which tends to crystallize; and or (ii) has a melting point T _m greater than 40 ° C; and or (iii) a polyester diol; and or (iv) from diols, in particular selected from the group consisting of ethanediol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, and mixtures thereof, and diacids, in particular dicarboxylic acids, preferably selected from the group consisting of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid and mixtures thereof, obtainable by condensation, in particular poly (tetramethylene adipate) (PTMA); and or (v) from cyclic esters, in particular ε-caprolactone, can be prepared by ring-opening polymerization; and or (vi) has an average molecular weight of 1000 to 5000, preferably 2000-3500 g / mol. The method according to any one of claims 1-3, characterized in that the polyol having at least one ionic or potentially ionic hydrophilic group (i) a polyol, in particular a polyether polyol, which has at least one, preferably exactly one, anionic or potentially anionic hydrophilic group; and or (ii) has an ionic group selected from the group consisting of sulfate, sulfonate, phosphate, phosphonate, carboxylate, and ammonium groups, as well as ionic heterocycles, especially nitrogen-containing, 5-6 membered heterocycles; and or (iii) has a potential ionic group selected from the group consisting of carboxylic acid and amino groups and uncharged heterocycles, especially nitrogen-containing, 5-6 membered heterocycles; and or (iv) an alkoxylated, in particular propoxylated, adduct of an alkenediol, especially 2-butene-1,4-diol, and a sulfite, especially a bisulfite; and or (V) has an average molecular weight in the range of 200 to 1000, preferably 300 to 500 g / mol. The method according to any one of claims 1-4, characterized in that the nonionic polyether polyol (i) a polypropylene glycol is homo- or copolymer, in particular a polypropylene glycol homopolymer or a polypropylene glycol / polyethylene glycol block copolymer, preferably having an ethylene oxide content of 45 mol% or less, more preferably 10 mol% or less; and or (ii) has an average molecular weight in the range of 1000 to 4000, preferably 1500 to 2500; and or (iii) has an HLB value <10, preferably <6, more preferably ≤3. The method according to one of the preceding claims, characterized in that the polyurethane prepolymer has an average molecular weight in the range of 3000-15000, in particular 5000 to 10000 g / mol. The method according to one of the preceding claims, characterized in that the content of ionic groups in the polyurethane prepolymer is not more than 20 milliequivalents, preferably not more than 10 milliequivalents per 100 g prepolymer. The method according to any one of the preceding claims, characterized in that the organic polyisocyanate is used in molar excess relative to the polyol mixture to obtain an NCO-functionalized polyurethane prepolymer. The method according to one of the preceding claims, characterized in that the organic polyisocyanate is a diisocyanate, in particular selected from the group consisting of aromatic diisocyanates, preferably diphenylmethane diisocyanate (MDI), polymeric MDI and / or toluene diisocyanate (TDI), and aliphatic diisocyanates, preferably Hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI) and / or methylene-4,4-bis (cyclohexyl) diisocyanate (H12MDI), or mixtures thereof. Aqueous polyurethane prepolymer dispersion obtainable by the process according to any one of claims 1-9. A process for preparing an aqueous polyurethane dispersion (PUD), characterized in that the polyurethane prepolymer in the aqueous polyurethane prepolymer dispersion of claim 10 is reacted with a chain extender to form an aqueous polyurethane dispersion. The method of claim 11, wherein the polyurethane prepolymer is an NCO-functionalized prepolymer and the prepolymer is reacted with a chain extender comprising at least two terminal NCO-reactive groups, especially a diamine or a diol. Aqueous polyurethane dispersion obtainable by the process according to claim 11 or 12. An adhesive, sealant or coating composition comprising the polyurethane dispersion of claim 13. Use of a polyurethane dispersion according to claim 13 as an adhesive, coating agent, sealant, fiber sizing or rheology modifier.

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